DefibViz: a visualization tool for the assessment of electrode parameters on transthoracic defibrillation thresholds

DefibViz is a software application developed for defibrillation simulation and visualization. It exploits both surface techniques and methods for the interactive exploration of volumetric datasets for the analysis of transthoracic defibrillation simulation results. DefibViz\ has a graphical user interface for the specification of the shape, size, position, and applied voltage of a defibrillator's electrodes. An option is provided for using 3-D slice plane widgets, which operate on the volumetric datasets, such that the distribution of the voltage gradient induced by an electric shock can be visually inspected in various tissues throughout the myocardium and torso. One goal of DefibViz is to enhance understanding of how electrode parameters relate to the change of the voltage gradient distribution throughout the heart, which may help lead to optimal defibrillator design. DefibViz; is significant, in that, it is built by using an open-source graphics and visualization framework providing a platform for subsequent modifiability and extensibility. Moreover, it integrates simulation and visualization techniques, which previously required the running of several independent software executables, into an enhanced, seamless, and comprehensive software application.     

Extracting isovolumes from three-dimensional torso geometry usingPROLOG

Three-dimensional (3D) finite element torso models are widely used to simulate defibrillation field quantities, such as potential, gradient and current density. These quantities are computed at spatial nodes that comprise the torso model. These spatial nodes typically number between 10⁵ and 10⁶, which makes the comprehension of torso defibrillation simulation output difficult. Therefore, the objective of this study is to rapidly prototype software to extract a subset of the geometric model of the torso for visualization in which the nodal information associated with the geometry of the model meets a specified threshold value (e.g., minimum gradient). The data extraction software is implemented in PROLOG, which is used to correlate the coordinate, structural and nodal data of the torso model. A PROLOG-based environment has been developed and is used to rapidly design and test new methods for sorting, collecting and optimizing data extractions from defibrillation simulations in a human torso model for subsequent visualization     

Measurement of defibrillation shock potential distributions andactivation sequences of the heart in three dimensions

The authors note that knowledge of the extracellular potential gradient field of the defibrillation shock and the cardiac-tissue response to the shock should lead to better understanding of the mechanism of defibrillation and stimulate improvement of defibrillation techniques. By measuring the potential distribution of the defibrillation shock throughout the heart and the location of the recording electrodes, the potential gradient field may be calculated. By recording local electrograms throughout the heart immediately before and after the shock, the tissue response to the shock can be evaluated     

Analysis of defibrillation efficacy from myocardial voltagegradients with finite element modeling

Increasing defibrillation efficacy by lowering the defibrillation threshold (DFT) is an important goal in positioning implantable cardioverter-defibrillator electrodes. Clinically, the DFT is difficult to estimate noninvasively. It has been suggested that the DFT relates to the myocardial voltage gradient distribution, but this relation has not been quantitatively demonstrated. We analyzed the relation between the experimentally measured DFT's and the simulated myocardial voltage gradients provided by finite element modeling. We performed a series of experiments in 11 pigs to measure the DFT's, and created and solved three-dimensional subject-specific finite element models to assess the correlation between the computed myocardial voltage gradient histograms and the DFT's. Our data show a statistically significant correlation between the DFT and the left ventricular voltage gradient distribution, with the septal region being more significant (correlation coefficient of 0.74) than other myocardial regions. The correlation between the DFT and the right ventricular and the atrial voltage gradient, on the other hand, is not significant.     

Volume rendering quantification algorithm for reconstruction of CT volume-rendered structures: Part I. Cerebral arteriovenous malformations

Volume rendering is a visualization technique that has important applications in diagnostic radiology and in radiotherapy but has not achieved widespread use due, in part, to the lack of volumetric analysis tools for comparison of volume rendering to conventional visualization techniques. The volume rendering quantification algorithm (VRQA), a technique for three-dimensional (3-D) reconstruction of a structure identified on six principal volume-rendered views, is introduced and described. VRQA involves three major steps: 1) preprocessing of the partial surfaces constructed from each of six volume-rendered images; 2) merging these processed partial surfaces to define the boundaries of a volume; and 3) computation of the volume of the structure from this boundary information. After testing on phantoms, VRQA was applied to CT data of patients with cerebral arteriovenous malformations (AVM's). Because volumetric visualization of the cerebral AVM is relatively insensitive to operator dependencies, such as the choice of opacity transfer function, and because precise volumetric definition of the AVM is necessary for radiosurgical treatment planning, it is representative of a class of structures that is ideal for testing and calibration of VRQA. AVM volumes obtained using VRQA are intermediate to those obtained using axial contouring and those obtained using CT-correlated biplanar angiography (two routinely used visualization techniques for treatment planning for AVM's). Applications and potential expansions of VRQA are discussed.     

Qt在光学芯片仿真软件设计中的应用

介绍了Qt控件库Qwt和QwtPlot3D的开发方法,并在光学芯片仿真系统中实现温度场分布数据可视化时得到应用,取得了良好的可视化效果.结果表明,Qt在CAD仿真软件开发中具有很强的优势.     

Computational studies of transthoracic and transvenousdefibrillation in a detailed 3-D human thorax model

A method for constructing and solving detailed patient-specific 3D finite element models of the human thorax is presented for use in defibrillation studies. The method utilizes the patient's own X-ray CT scan and a simplified meshing scheme to quickly and efficiently generate a model typically composed of approximately 400,000 elements. A parameter sensitivity study on one human thorax model to examine the effects of variation in assigned tissue resistivity values, level of anatomical detail included in the model, and number of CT slices used to produce the model is presented. Of the seven tissue types examined, the average left ventricular (LV) myocardial voltage gradient was most sensitive to the values of myocardial and blood resistivity. Incorrectly simplifying the model, for example modeling the heart as a homogeneous structure by ignoring the blood in the chambers, caused the average LV myocardial voltage gradient to increase by 12%. The sensitivity of the model to variations in electrode size and position was also examined. Small changes (<2.0 cm) in electrode position caused average LV myocardial voltage gradient values to increase by up to 12%. It is concluded that patient-specific 3D finite element modeling of human thoracic electric fields is feasible and may reduce the empiric approach to insertion of implantable defibrillators and improve transthoracic defibrillation techniques     

Rigid and flexible thin-film multielectrode arrays for transmuralcardiac recording

Thin-film transmural cardiac multielectric arrays were fabricated using integrated-circuit processing techniques. Several substantial improvements were achieved over conventional handmade arrays such as a smaller cross-sectional area, a larger number of recording sites per needle, more accurately controlled size and spacing of the recording sites, smaller bipolar spacings, and higher throughout yield. These advantages allow for a higher density of closely spaced bipolar electrodes capable of monitoring complex voltage and gradient fields present during ventricular fibrillation and defibrillation. Both rigid and flexible arrays were fabricated and used in the acquisition of transmural electrical signals. The rigid multielectrode arrays were made of gold electrodes on a molybdenum substate, and the flexible arrays of silver and gold electrodes on a polyimide substrate. In vitro and in vivo testing of the thin-film transmural cardiac multielectrode arrays indicates that there are no adhesion or delamination problems observed during acute studies, no implantation difficulties, and that unipolar and bipolar recordings during normal sinus rhythm and injury potentials in unipolar recordings are similar to those obtained using the handmade electrodes.     

An investigation of the importance of myocardial anisotropy infinite-element modeling of the heart: methodology and application to theestimation of defibrillation efficacy

Finite-element (FE) modeling has been widely used in studies of bioelectric phenomena of tissues, including ventricular defibrillation. Most FE models, whether built from anatomical atlases or subject-specific tomographic images, treat the myocardium as an isotropic tissue. However, myocardium has been experimentally shown to have significant anisotropy in its resistivities, although myocardial fiber directions are difficult to measure on a subject-specific basis. In this paper, we: 1). propose a method to incorporate a widely known myocardial fiber direction model to a specific individual and 2). assess the effects of myocardial anisotropy on myocardial voltage gradients computed for a study of implantable defibrillators. The thoracic FE model was built from CT images of a young pig, and the myocardial fiber structures were incorporated via elastic mapping. Our results demonstrate a good mapping of geometry between the source and target hearts with an average root-mean-square error of less than 2.3 mm and a mapped fiber pattern similar to those known to exist in vivo. With the mapped fiber information, we showed that the estimated minimal myocardial voltage gradient over 80% of the myocardium differs by less than 10% between using an isotropic and anisotropic myocardial models. Thus, myocardial anisotropy is expected to have only a small effect on estimates of defibrillation threshold obtained from computed voltage gradients. On the other hand, anisotropy may be essential if defibrillation efficacy is analyzed by transmembrane voltage of the myocardial cells.     

基础物理实验中RC微积分电路的Multisim仿真

基于探索RC微积分电路仿真实验技术的目的,采用Multisim10仿真软件对RC微积分电路的工作波形进行了仿真实验测试,给出了几种Multisim仿真实验方案,分析了输出电压与输入电压之间的运算关系,分析了电路时间常数与输入信号周期之间的关系及矩形电压输入时输出电压的波形形式,结论是仿真实验可直观形象地描述RC微积分电路的工作过程。将电路的硬件实验方式向多元化方式转移,利于培养知识综合、知识应用、知识迁移的能力,使电路分析更加灵活和直观。     

微流控液体变焦透镜内芯结构的电场仿真

主要研究了圆台型内芯的液体变焦透镜的电场分布。通过使用COMSOL软件（多物理场分析软件）建立相应模型,改变圆台内芯结构的角度、电压和圆台半径等参数来观察其内芯中的电场分布情况。根据仿真结果对比于圆柱内芯结构（即圆台型结构的角度为零）,圆台型结构更符合实际应用的要求。     

Qwt类库在二维云图绘制中的应用

介绍了Qwt类库在数值模拟软件中的开发方法。首先简要介绍了开发工具Qt和图形库Qwt,然后给出数值模拟软件的可视化分析,最后重点阐述了实现Qwt云图绘制功能的关键技术。通过Qwt在软件中的应用,实现了计算数据的可视化,并取得了良好的云图可视化效果。基于Qwt的开发结果表明,Qwt在数值模拟软件后处理的开发中具有很强的优势。     

热电堆型激光功率计设计与仿真

针对紫外、可见、红外等激光器输出功率测试需求,提出一种由传热体、吸收层、绝缘层和热电偶构成的热电堆型激光功率计.结合热效应和塞贝克效应理论,采用Solidworks三维设计软件构建不同关键结构尺寸的模型,通过ANSYS Workbench仿真软件建立了热电耦合仿真分析模型,分析关键结构尺寸参数对输出电压以及温度分布的影...     

GaN_Si npn HBT特性研究

采用二维器件仿真软件对GaN/Si异质结双极晶体管进行了特性仿真研究.对GaN/Si异质结双极晶体管建立了合理准确的物理模型,包括不完全电离模型、能带模型、能带变窄模型、迁移率模型与复合模型.结果表明,GaN/Si异质结开启电压为2.5 eV.在Ib=0.2 mA时,电流放大倍数为100倍.击穿电压为900V,使其在大功率器件方面有很大应用前景.最高截止频率为100 GHz,使其可工作在射频和微波频段.     

基于EDA技术的压控LC振荡器的设计与实现

根据压控LC振荡器的基本原理，提出了以EDA（Electronic Design Automation，电子设计自动化）软件MAX＋PLUSⅡ为基础压控LC振荡器设计的技术方案，详细阐述了系统的设计要求、设计技巧、设计方案，并进行了系统仿真和硬件测试。     

A unified theory for frequency-domain simulation and sensitivityanalysis of linear and nonlinear circuits

The harmonic balance technique from nonlinear simulation is extended to nonlinear adjoint sensitivity analysis. This provides an efficient tool for the otherwise expensive but essential gradient calculations in design optimization. The hierarchical approach widely used for circuit simulation, is generalized to sensitivity analysis and to computing responses in any subnetwork at any level of the hierarchy. Important aspects of frequency-domain circuit computer-aided design (CAD) such as simulation and sensitivity analysis, linear and nonlinear circuits, hierarchical and nonhierarchical approaches, voltage and current excitations, or open- and short-circuit terminations are unified in this general framework. The theory provides a basis for the next generation of microwave CAD software. It takes advantage of mature techniques such as syntax-oriented hierarchical analysis, optimization, and yield-driven design to handle nonlinear as well as linear circuits. The sensitivity analysis approach has been verified by a MESFET mixer example, exhibiting a 90% saving of CPU time over the prevailing perturbation method     

多源异构数据的多维决策分析与可视化方法

随着各行业各业务信息系统的不断建设与使用,行业积累了越来越多的多源异构的历史数据,快速发现有价值信息已成为一个主要的研究方向.以气象数据为例,针对气象历史数据的海量多源异构特点,结合气象业务多维决策分析与可视化的具体需求,提出一种面向多源异构数据的多维决策分析与可视化方法,该方法实现了多源异构数据的自动抽取与转换,多用户的在线多维决策分析模型设计以及分析结果的直观多形式可视化技术.通过该方法研制的系统在嘉定气象局业务中得到成功应用,有效提升了对气象数据的理解和利用水平;同时对其他行业多源异构数据的处理具有很好的借鉴作用.     

Visualization: the look of reality

The need to understand behavior, be it of objects, systems, or organisms, bred the need to simulate it visually, which has been in turn the prime catalyst in the use of computer graphics. A 1987 National Science Foundation report helped give the term “visualization” a place in the computing lexicon, and by now the field has generated a multibillion-dollar industry in software, hardware, and related equipment. Visualization is the process of making visible what is hard or impossible to see in the physical world. It therefore embraces the display of volumetric data and representations of fields and mathematical phenomena, plus distributed visual processing the use of animation (to add the dimensions of time and motion to a subject), and the mating of visualization capabilities with software for such tasks as finite-element analysis. The author discusses visualization and its benefits and applications     

电磁信号环境仿真与可视化分析系统

电磁信号环境仿真与可视化分析系统集成了战场电磁信号环境仿真功能和电磁信号可视化分析功能。一方面,针对战场电磁环境的构成要素及其变化特征,建立粗颗粒和细颗粒两种粒度的信号模型,并建立信号的空间传播模型,实现电磁信号环境的动态仿真;另一方面,综合利用计算机图形图像处理技术、高性能计算技术等,实现战场电磁态势三维显示和电磁信号环境的可视化分析。本文对系统的功能、总体结构、软件结构、硬件结构和工作流程等方面进行了详细的介绍,并对系统进行了应用实例分析。从应用效果看,系统可作为电子战军官、操作员进行战场电磁态势分析以及电子侦察情报分析训练的仿真工具。     

基于LabWindows/CVI的电压闪变测量研究

电压闪变是衡量电能质量的一个重要参数,对其进行准确测量具有非常重要的现实意义。虚拟仪器是测量仪器和计算机紧密结合的一种新型的测量仪器。针对此,利用LabWindows/CVI设计了电压闪变测量模块,给出了测量原理、软硬件实现方法及部分关键代码。仿真和应用表明,所开发的电压闪变测量模块性能达到了IEC的闪变仪测量标准。